System and method for pressure mixing bone filling material

ABSTRACT

A method for treating a vertebral bone comprises providing a bone filling material and mixing the bone filling material in a vessel to form a bone augmentation material. The method further comprises pressurizing the vessel with a pressurization source to retain a plurality of voids within the bone augmentation material. The method further includes inserting a material delivery device into the vertebral bone and injecting the bone augmentation material with the retained plurality of voids from the material delivery device and into the vertebral bone.

CROSS REFERENCE

The related applications, incorporated by reference herein, are:

U.S. Utility Patent Application Ser. No. (Attorney Docket No.P0026129.00/31132.592), filed on Jan. 12, 2007 and entitled “System andMethod For Forming Porous Bone Filling Material” and

U.S. Utility Patent Application Serial No. (Attorney Docket No.P0026125.00/31132.590), filed on Jan. 12, 2007 and entitled “System andMethod For Forming Bone Filling Materials With Microparticles”.

BACKGROUND

Bone cements and other bone filling materials are currently usedthroughout the skeletal system to augment or replace bone weakened orlost to disease or injury. One example of a treatment that includes theadministration of bone filling material is vertebroplasty. Duringvertebroplasty, the cancellous bone of a vertebral body is supplementedwith bone filling material. Frequently, the available bone fillingmaterials do not possess material properties similar to the native bone.Materials, systems, and methods are needed to form and deliver bonefilling materials that may be selectively matched to the natural boneundergoing treatment.

SUMMARY

In one embodiment, a method for treating a vertebral bone comprisesproviding a bone filling material and mixing the bone filling materialin a vessel to form a bone augmentation material. The method furthercomprises pressurizing the vessel with a pressurization source to retaina plurality of voids within the bone augmentation material. The methodfurther includes inserting a material delivery device into the vertebralbone and injecting the bone augmentation material with the retainedplurality of voids from the material delivery device and into thevertebral bone.

In another embodiment, a bone augmentation system comprises a mixingvessel at least partially filled with a bone filling material, themixing vessel comprising a mixing element. Mixing the bone fillingmaterial with the mixing element creates a void filled bone augmentationmaterial. A pressurization source is connected to the mixing vessel andadapted to prevent at least some voids in the void filled boneaugmentation material from escaping. A dispensing instrument comprises adispensing reservoir and is adapted to receive the void filled boneaugmentation material. The dispensing instrument further comprises acannulated member adapted to deliver the void filled bone augmentationmaterial into a body region adjacent cancellous bone.

In another embodiment, a method of augmenting a bone comprises mixing abone filling material in a mixing vessel to generate a bone augmentationmaterial comprising a plurality of voids, elevating the pressure in themixing vessel above atmospheric pressure, retaining at least a portionof the plurality of voids within the bone augmentation material,injecting the bone augmentation material into the bone, and allowing thebone augmentation material to set to a hardened and porous conditionwithin the bone.

Additional embodiments are included in the attached drawings and thedescription provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart for a process of forming a modulated boneaugmentation material according to one embodiment of the disclosure.

FIG. 2 is a schematic diagram of a material preparation system accordingto one embodiment of the present disclosure.

FIG. 3 is a sagittal view of a section of a vertebral column.

FIG. 4 is a sagittal view of a section of a vertebral column undergoinga vertebroplasty procedure using a porous bone augmentation material.

FIGS. 5-6 are detailed views of the procedure of FIG. 4.

FIG. 7 is a sagittal view of a section of a vertebral column with anintervertebral disc treated with porous bone filling material.

DETAILED DESCRIPTION

The present disclosure relates generally to devices, methods andapparatus for augmenting bone, and more particularly, to methods andinstruments for augmenting bone with a porous material. For the purposesof promoting an understanding of the principles of the invention,reference will now be made to the embodiments, or examples, illustratedin the drawings and specific language will be used to describe the same.It will nevertheless be understood that no limitation of the scope ofthe invention is thereby intended. Any alterations and furthermodifications in the described embodiments, and any further applicationsof the principles of the invention as described herein are contemplatedas would normally occur to one skilled in the art to which the inventionrelates.

Referring first to FIG. 1, the reference numeral 10 refers to a methodfor forming a modified or modulated bone augmentation material that maybetter correspond to the material properties, including the modulus ofelasticity, of a target bone region as compared to unmodulated bonefilling material such as bone cement. At steps 12 and 14 first andsecond components of a bone filling material may be selected. As shownin FIG. 2, a material preparation system 30 may receive a firstcomponent of a bone filling material 32 and a second component of bonefilling material 34. This embodiment describes the use of a twocomponent bone filling material such as polymethylmethacrylate (PMMA),which is formed from a PMMA powder and a PMMA monomer. It is understoodthat in alternative embodiments, suitable bone filling material may besingle component materials or have more than two components. In additionto PMMA bone cement, suitable bone filling materials may include calciumphosphate bone cement, calcium sulfate compounds, calcium aluminatecompounds, aluminum silicate compounds, hydroxyapatite compounds, insitu curable ceramics or polymers, or other flowable materials thatbecome more rigid after delivery. Generally, before it is modified, thebone filling material in a hardened state may have a higher modulus ofelasticity than the target bone region.

Referring again to FIGS. 1 and 2, at step 16, the first component 32 andthe second component 34 may be deposited in a mixing vessel 36 whichcomprises a mixing mechanism 38. The mixing vessel 36 may be sealable.The mixing mechanism 38 may be activated to mix the components 32, 34.Suitable mixing mechanisms may include an agitator having a rotarymixing blade, an aerator, static mixing elements or any other deviceoperable to mix a bone filling material. Electric, manual, and pneumaticmixing mechanisms may be suitable for mixing the bone filling material.It is understood that although the mixing mechanism 38 is depicted aslocated within the mixing vessel 36, all or parts of the mixingmechanism may be located outside of the mixing vessel, but still providea mixing action to the contents of the mixing vessel. An aerator or amagnetic mixing device may be examples of mixing mechanisms locatedoutside of the mixing vessel.

As the components 32, 34 of the bone filling material are mixed, gaseousvoids, such as air bubbles, may form from, for example, the mixingaction of the mixing mechanism 38 and/or the chemical reaction of thefirst and second components 32, 34. The gaseous voids may becomedispersed throughout the mixture of bone filling materials 32, 34 toform a porous modulated bone augmentation material. It is understoodthat the gaseous voids may contain air or other gaseous substances.

At step 18, to prevent the gaseous voids from rising through andescaping from the bone augmentation material, the contents of the mixingvessel 36 may be pressurized by a pressurization source 40 connected tothe mixing vessel 36. The pressurization source 40 may raise andmaintain the pressure in the mixing vessel at a level greater thanatmospheric pressure. In one embodiment, the pressurization source is apump that pumps outside air or other gaseous substances into theotherwise sealed mixing vessel. In another embodiment, thepressurization source is a container of compressed gas, such as acartridge of compressed carbon dioxide, nitrogen, or oxygen. Otherpressurization sources connectable to or integral with the mixing vesselmay also be suitable.

The speed and type of the mixing mechanism 38, the shape of the mixingmechanism and mixing vessel 36, the amount of pressure provided by thepressurization source 40, and the duration of the mixing are among thefactors that may contribute to the size and density of the voidformation in the fluid modulated bone augmentation material, andultimately the size and density of the pores that are formed in thehardened modulated bone augmentation material. Larger pores may impart alower modulus than the same quantity of smaller pores. A higher densityof pores may impart a lower modulus to the bone filling material thanwould a less dense array of pores of the same size and materialproperties.

The pressurization source 40 may be adjustable to control the size anddensity of the formed voids. For example, pressurization may begradually reduced during the mixing process as the increasing viscosityof the bone filling material traps a greater quantity of voids. Apressure gauge may be used to monitor the pressurization and to controlthe adjustment of the pressurization source 40.

The mixing and pressurization may continue until the concentration ofbubbles in the liquid bone augmentation material is sufficient to lowerthe overall modulus of elasticity of the final cured or hardenedmodulated bone augmentation material to a level that more closelymatches the modulus of the target bone region or that at least mayreduce the risk of damage to the adjacent bone that could otherwise becaused by the unmodulated bone cement. In certain patients, it may bedesirable to reduce the modulus of elasticity to a level lower thannatural cancellous bone. For example, a modulus of elasticity forhardened bone augmentation material that is less than five times that ofcancellous bone may be suitable for some patients.

The desired size and density of the pores may be dependent upon the sizeof the target bone region and characteristics of the patient includingthe age, bone density, body mass index, or health of the patient. Forexample, an elderly osteoporotic vertebroplasty patient may require amore reduced modulus bone augmentation material than would a younghealthy trauma victim undergoing a similar procedure. The size of thepores may be selected based upon the patient and controlled bypressurization. For example, 90% of the pores may be in the range of 1to 2000 microns in diameter. Other suitable pore sizes may range from 10to 1000 microns.

Other additives may be added to the bone filling material during thepreparation of the bone filling material or during the pressurizedmixing. Additives that include radiocontrast media may be added to thebone filling material to aid in visualizing the bone augmentationmaterial with imaging equipment. Suitable radiocontrast materials mayinclude barium sulfate, tungsten, tantalum, or titanium. Additives thatinclude osteoconductive or osteoinductive materials may be added topromote bone growth into the hardened bone augmentation material.Suitable osteoconductive materials may include hydroxyapatite (HA),tricalcium phosphate (TCP), HA-TCP, calcium phosphate, calcium sulfate,calcium carbonate, and/or bioactive glasses. Suitable osteoinductivematerials may include proteins from transforming growth factor (TGF)beta superfamily, or bone-morphogenic proteins, such as BMP2 or BMP7.Pharmacological agents may be added to promote healing and prevent orfight infection. Suitable pharmacological additives may includeantibiotics, anti-inflammatory drugs, or analgesics.

Referring again to FIG. 1, at step 20, the modulated bone augmentationmaterial, including any additives, may be delivered into a target boneregion in a patient's anatomy. The modulated bone augmentation materialmay be transferred to a delivery system, such as a syringe or a threadedmaterial dispensing system prior to delivery into the target boneregion. In alternative embodiments, the bone filling material may bemixed and pressurized in the same container that will be used todispense the mixture such that a material transfer becomes unnecessary.

Although the target bone region will often be in a bone, other boneregions, such as joints, may receive the modulated bone augmentationmaterial to, for example, promote fusion. Examples of target boneregions may be fractured cortical or cancellous bone, osteoporoticcancellous bone, or degenerated intervertebral discs. By matching themodulated bone augmentation material to the material properties of theadjacent bone, complications associated with unaltered, high modulusbone cements may be minimized. In particular, matching the materialproperties may provide a uniform stress distribution, minimizingsignificant stress concentrations that may pose a fracture risk toadjacent bone.

Referring now to FIG. 3, in one embodiment, a modulated boneaugmentation material formed by method 10 may be used to augment orreplace portions of a vertebral column. The reference numeral 50 refersto a healthy vertebral joint section of a vertebral column. The jointsection 50 includes adjacent vertebrae 52, 54 having vertebral bodies56, 58, respectively. An intervertebral disc 60 extends between thevertebral bodies 56, 58. Although FIG. 3 generally depicts a lumbarregion of the spine, it is understood that the systems, materials, andmethods of this disclosure may be used in other regions of the vertebralcolumn including the thoracic or cervical regions.

Referring now to FIGS. 4-6, due to traumatic injury, cancer,osteoporosis or other afflictions, the vertebral body portion 58 of thevertebra 54 may begin to collapse, causing pain and loss of bone height.One procedure for restoring the vertebral height, reducing pain, and/orbuilding mass is known as vertebroplasty. In a vertebroplasty procedureaccording to one embodiment of this disclosure, a stylet or othersharpened instrument (not shown) may be inserted into an injectioninstrument such as a cannula 62 and arranged so that a sharpened tipprotrudes through the end of the cannula. The assembled stylet andcannula 62 may then be inserted through a pedicle of the vertebra 54 andinto the cancellous bone of the vertebral body 58. This insertion may beguided through the use of fluoroscopy or other imaging modalities. Withthe cannula 62 in place in the vertebral body 58, the stylet may bewithdrawn leaving the cannula in place to serve as a pathway fordelivering instruments or materials into the bone. In alternativeembodiments, a surgical needle having a cannulated body and a pointedtip may be used to access the vertebral body.

Following the method 10, described above, a modulated bone augmentationmaterial 64 comprised of bone cement 66 and gaseous voids 68 may beformed and transferred to a delivery system 70. The delivery system 70may be a conventional syringe, having a material reservoir and a plungermechanism movable therethrough, or a more sophisticated threadedinjection system such as the type covered by, for example, U.S. Pat. No.6,348,055 which is incorporated by reference herein. Other types ofmaterial delivery systems may also be suitable. The delivery system 70may be actuated, such as by moving the plunger mechanism into thematerial reservoir, to move the bone augmentation material 64 throughthe cannula 62 and into the vertebra 54 where the mixture may flow intothe interstices of the cancellous bone of the vertebral body 58 as shownin FIG. 6. It is understood that the gaseous voids 68 shown in FIG. 6are not necessarily to scale but rather are merely exemplary of therandom disbursement of the gaseous voids which will later form poreswithin the hardened bone augmentation material. As described above,within any given mixture of modulated bone augmentation material, thepores may have different sizes and/or properties. Further, the densityof pores may be determined based upon the amount the original bonefilling material must be modified to achieve an acceptable modulatedbone augmentation material.

With the gaseous voids 68 distributed throughout the bone cement 66, themodulated bone augmentation material 64 may be cured or otherwiseallowed to harden within the vertebral body 58. The gaseous voids 68 mayremain suspended in the hardened bone cement 66, forming pores whichreduce the overall stiffness of the modulated bone augmentation material64. The modulus of elasticity of the hardened modulated boneaugmentation material 64 may be lower than that of the unmodulatedhardened bone filling material 66, alone, and closer to the modulus ofelasticity of the cancellous bone of the vertebral body 58 than that ofthe hardened bone filling material alone. Thus, the material 64 createsa more uniform stiffness in the vertebral body 58, avoiding thesignificant alterations in stress distribution that would be associatedwith the use of bone cement alone. The more uniform stiffness in thevertebral body 58 may lower the risk for fracture in the adjacentvertebrae.

Although the use of the modulated bone augmentation material 64 has beendescribed for use in a vertebroplasty procedure, it is understood thatin alternative vertebral treatments, channels or voids may be formed inthe vertebral body using probes, balloons, drills, cutting blades orother devices. In these embodiments, the mixture of gaseous bubbles andbone filling material may be used to fill the preformed voids orchannels. The resulting reduced modulus material may be particularlyeffective in these embodiments as the otherwise unmodulated, largeconcentrations of bone cement accumulating in the preformed voids maygive rise to significant alteration is the stress distribution.

Although the use of modulated bone augmentation material has beendescribed primarily for vertebral body applications, it is understoodthat the same modulated material may be used for other procedures wherereduced modulus bone cement may be desirable. For example, the modulatedmaterial may be useful for fracture repair.

In one alternative embodiment, a modulated bone augmentation material71, including gaseous bubbles 72, may be created using the method 10 andmay be used to fuse the joint section 50. The fusion of the joint 50 maybe accomplished using conventional fusion techniques includingtransforaminal lumbar interbody fusion (TLIF), posterior lumbarinterbody fusion (PLIF), or anterior lumbar interbody fusion (ALIF)procedures. Such techniques may involve the use of cages or otherintervertebral spacers to maintain the height of the disc space. As asupplement or replacement for the bone graft or bone cement that wouldotherwise be used in a spinal fusion procedure, the modulated material71 may be injected into the disc 60 or the disc space remaining afterthe removal of disc 60. The modulated material 71 may flow intocrevices, voids, or prepared areas of the adjacent vertebral endplates.After hardening, the material 71 may have a modulus of elasticitysimilar to that of the adjacent endplates of the vertebrae 52, 54, or atleast lower than unmodulated bone cement. Use of the modulated material71 may reduce the risk of the hardened material subsiding into theendplates of the adjacent vertebrae 52, 54.

Although only a few exemplary embodiments have been described in detailabove, those skilled in the art will readily appreciate that manymodifications are possible in the exemplary embodiments withoutmaterially departing from the novel teachings and advantages of thisdisclosure. Accordingly, all such modifications and alternative areintended to be included within the scope of the invention as defined inthe following claims. Those skilled in the art should also realize thatsuch modifications and equivalent constructions or methods do not departfrom the spirit and scope of the present disclosure, and that they maymake various changes, substitutions, and alterations herein withoutdeparting from the spirit and scope of the present disclosure. It isunderstood that all spatial references, such as “horizontal,”“vertical,” “top,” “upper,” “lower,” “bottom,” “left,” “right,”“anterior,” “posterior,” “superior,” “inferior,” “upper,” and “lower”are for illustrative purposes only and can be varied within the scope ofthe disclosure. In the claims, means-plus-function clauses are intendedto cover the elements described herein as performing the recitedfunction and not only structural equivalents, but also equivalentelements.

1-22. (canceled)
 23. A bone augmentation system comprising: a mixingvessel at least partially filled with a bone filling material, themixing vessel comprising a mixing element, wherein mixing the bonefilling material with the mixing element creates a bone augmentationmaterial including a plurality of voids; a pressurization sourceconnected to the mixing vessel and adapted to prevent at least somevoids in the bone augmentation material from escaping; a dispensinginstrument comprising a dispensing reservoir adapted to receive the boneaugmentation material and comprising a cannulated member adapted todeliver the bone augmentation material into a body region adjacentcancellous bone.
 24. The bone augmentation system of claim 23 furthercomprising: a control mechanism operable to regulate the pressurizationsource.
 25. The bone augmentation system of claim 23 wherein thepressurization source is an air pump.
 26. The bone augmentation systemof claim 23 wherein the pressurization source is a compressed gascartridge.
 27. The bone augmentation system of claim 23 wherein themixing mechanism comprises a rotatable mixing blade.
 28. The boneaugmentation system of claim 23 wherein the mixing mechanism is anaerator.
 29. The bone augmentation system of claim 23 wherein thepressurization source generates a vessel pressure greater than anatmospheric pressure within the mixing vessel. 30-32. (canceled)
 33. Thebone augmentation system of claim 23 wherein the mixing vessel issealed.
 34. The bone augmentation system of claim 23 wherein the mixingvessel is sealed and the pressurization source is a pump that pumpsoutside air or other gaseous substances into the mixing vessel.
 35. Thebone augmentation system of claim 23 wherein the mixing mechanismcomprises static mixing elements.
 36. The bone augmentation system ofclaim 23 further comprising a pressure gauge configured to monitorpressure within the mixing vessel.
 37. The bone augmentation system ofclaim 23 wherein the dispensing instrument comprises a plunger mechanismthat is movable through the dispensing reservoir.
 38. The boneaugmentation system of claim 23 wherein the pressurization source isconfigured to generate a vessel pressure greater than an atmosphericpressure within the mixing vessel as the mixing element mixes the bonefilling material to create the bone augmentation material.
 39. A boneaugmentation system comprising: a bone filling material; a mixing vesselat least partially filled with the bone filling material, the mixingvessel comprising a mixing element configured to mix the bone fillingmaterial to create a bone augmentation material including a plurality ofvoids; a pressurization source connected to the mixing vessel andadapted to generate a vessel pressure greater than an atmosphericpressure within the mixing vessel to prevent at least some voids in thebone augmentation material from escaping; a dispensing instrumentcomprising a dispensing reservoir adapted to receive the boneaugmentation material and comprising a cannulated member adapted todeliver the bone augmentation material into a body region adjacentcancellous bone; and a control mechanism operable to regulate thepressurization source to control pressure within the mixing vessel. 40.The bone augmentation system of claim 39 wherein the mixing vessel issealed and the pressurization source is a pump that pumps outside air orother gaseous substances into the mixing vessel.
 41. The boneaugmentation system of claim 39 wherein the pressurization source isconfigured to generate the vessel pressure greater than the atmosphericpressure within the mixing vessel as the mixing element mixes the bonefilling material to create the bone augmentation material.
 42. The boneaugmentation system of claim 39 wherein the bone filling materialcomprises a component selected from a group consisting of:polymethylmethacrylate, calcium phosphate, calcium sulfate andhydroxyapatite.
 43. The bone augmentation system of claim 39 furthercomprising the bone augmentation material, wherein the bone augmentationmaterial comprises plurality of voids each having a diameter between 1and 2000 microns.
 44. The bone augmentation system of claim 39 whereinthe bone augmentation material comprises osteoinductive materialsselected from a group consisting of: proteins from transforming growthfactor (TGF) beta superfamily, bone-morphogenic proteins, BMP2 and BMP7.45. A bone augmentation system comprising: a bone filling materialcomprising a component selected from a group consisting of:polymethylmethacrylate, calcium phosphate, calcium sulfate andhydroxyapatite; a sealed mixing vessel at least partially filled withthe bone filling material, the mixing vessel comprising a mixing elementconfigured to mix the bone filling material to create a boneaugmentation material including a plurality of voids each having adiameter between 1 and 2000 microns; a pressurization source connectedto the mixing vessel and comprising a pump adapted to pump outside airor other gaseous substances into the mixing vessel to generate a vesselpressure greater than an atmospheric pressure within the mixing vesselas the mixing element mixes the bone filling material to prevent atleast some voids in the bone augmentation material from escaping; adispensing instrument comprising a dispensing reservoir adapted toreceive the bone augmentation material and comprising a cannulatedmember adapted to deliver the bone augmentation material into a bodyregion adjacent cancellous bone; a control mechanism operable toregulate the pressurization source to control pressure within the mixingvessel; and the bone augmentation material, wherein the boneaugmentation material comprises osteoinductive materials selected from agroup consisting of: proteins from transforming growth factor (TGF) betasuperfamily, bone-morphogenic proteins, BMP2 and BMP7.